A Wide Tuning Range Bandpass Filter Using Unequal Width Parallel-Coupled Dual- Mode Resonator

This paper presents a novel frequency reconfigurable microstrip bandpass filter (BPF) with wide tuning range based on parallel-coupled dual-mode resonator. The addition of the dual-mode resonator substantially suppresses the unwanted passband close to 2f
0
. In particular, each of the unequal width parallel coupled lines has a varactor diode connected to one end of the coupled-line while the other end is connected to a dual-mode resonator. A two-pole BPF was designed and fabricated and tested demonstrating 1.37:1 center frequency tuning. Furthermore the insertion loss within the frequency tuning range is 1.3 to 1.7 dB and the return loss greater than 20 dB.